MDR1 gene expression is an important prognostic marker in many human cancers. This application focuses on the underlying mechanisms responsible for regulating the expression of MDR1, particularly involving the NF-IL6 family of transcriptional regulators. Aim 1. To Study the Role of NF-IL6 in Activating or Suppressing MDR1 Expression. The hypothesis is that altered expression of NF-IL6 family members in human cancer cells may be responsible for MDR1 activation in these cells. Experimental approaches will include co-transfection of MDR1 promoter constructs and different forms of NF-IL6, quantitative analysis of NF-IL6 family members in nuclear and cytoplasmic extracts, and studies of the phosphorylation status of NF-IL6 species in cellular models. Aim 2. To Study Protein-Protein Interactions Mediated by NF-IL6 in MDR1. An NF-IL6-2 interacting site was mapped in MCF-7 cells within -128 to -75 of the MDR1 P1 promoter, a region which lacks NF-IL6 binding motifs. NF-IL6 may activate the MDR1 promoter through multiple interaction sites. Physical interactions among NF-IL6 family members, the Y-box-associated factors (NF-Y and YB-1), and AP1 (c-fos and c-jun) will be verified in vitro by GST pull down experiments utilizing a GST-NF-IL6 fusion protein to precipitate factors in nuclear extracts of MDR cell lines. Once protein interactions are established, their functional role in regulating the chromosomal MDR1 gene will be examined in stable transfectants containing MDR1 constructs. Aim 3. To Investigate a Novel Activator Involved in MDR1 Regulation. The hypothesis is that that there is a novel binding protein, other than NF-IL6, responsible for maintaining basal promoter activity in MCF-7 cells. The plan is to identify the protein and its gene binding to the -148 to -140 element by mobility shift assays as well as the yeast one-hybrid system. Sense and antisense cDNAs for this binding protein will be transfected into both MCF-7 and MCF-7/ADR cells to test their capacity to activate or modulate MDR1 expression. Aim 4. To Study MDR1 Regulation in Clinical Specimens. The focus will be on acute myeloid leukemia (AML) as a clinical model for MDR1 expression. MDR1 will be analyzed by rtPCR and flow cytometry. NF-IL6 members will be quantitatively analyzed in both nudear and cytoplasmic extracts of AML.